Highly selective ppb-level detection of NH3 and NO2 gas using patterned porous channels of ITO nanoparticles

Abstract

We demonstrate the formation of micro-patterned porous electronic channels of tin-doped indium oxide nanoparticles (ITO NPs) and their utilization as sensor transducers for the detection of NH3 and NO2 gas in air. The ITO NP channels were formed by dipping a molecularly patterned solid substrate into an ITO NP suspension and then pulling it vertically at a precisely controlled speed. The ITO NPs were self-assembled on the intended regions with high definition, as the NPs were selectively adsorbed on the polar SiO2 regions avoiding the nonpolar regions. The thickness of the assembled ITO NP patterns could be modulated by controlling the pulling speed. The NPs formed a dense percolated network through which current could flow without any post-treatment such as heat annealing. By forming electrodes on the assembled ITO NP patterns, we fabricated sensor transducers for the detection of ammonia and nitrogen dioxide. The sensor showed a highly sensitive detection of NH3 and NO2 gas down to ppb-level. Furthermore, the sensor response changed in opposite direction to reducing NH3 and oxidizing NO2 gases, which shows that our sensor can be utilized in the selective detection of NH3 and NO2.